1. Field of the Invention
This invention relates to optical glass filters comprising a filter glass which shows an optimized transmission spectrum with high transmission in the wave length range of 300 to 400 nm and very low transmission in the visible wave length range. The glass is characterized by an especially high optical quality and is excellently suitable as optical filter for generating UV light without a proportion of visible light.
2. Description of Related Art
Glass filters are known from prior art. So for example the document DE 3 643 421 A1 describes lead- and tin-containing glasses which are used in the case of filtering of UV light sources in the emission range of 200-1100 nm. In this document also the solarization—thus the influence of long-lasting UV irradiation onto the adsorption properties—is described. Lead and tin oxide are used for decreasing the tendency to solarization. Due to its ecologically damaging properties today lead is still no longer accepted in filter glasses. The difference of the glasses of the present invention and the glasses described in this mentioned document is that in the glasses of the present invention colored oxides in special ratios are used which results in advantageous transmission properties and solarization stability even without the use of lead and tin.
EP 0 522 859 A2 describes different filter glasses wherein the glass mentioned in the abstract as the second glass already due to its content of silica is considerably different from the glasses which are used in the present invention. Also the glass mentioned as the first glass in this document is different from the glasses which are used in the filter of the present invention. The glasses mentioned in this document comprise copper halides in a proportion of at least 0.05% by weight. Allegedly, the other components in the glass are not of importance. The glasses described are allowed to contain lead in considerable amounts. The relevance of the use of the colored components nickel oxide and cobalt oxide has not been understood. The amounts of boron oxide used are very high.
JP H0-6279057 A describes glasses which do not comprise the necessary proportions of the colored components nickel oxide and cobalt oxide. In addition, the content of lithium oxide and sodium oxide is relatively high which compromises the chemical resistance.